The invention relates to a pressure medium-actuated working cylinder in which the piston, on running into an end position, is braked by throttling of the pressure medium outflow from the shrinking cylinder chamber. As a result of the throttling of the output flow of pressure medium a pressure is built up in the shrinking cylinder chamber that generates a force on the piston that is directed against the movement of the piston.
What is referred to as the damping pressure building up in the cylinder chamber should, in this case, not exceed a maximum value which is from 1.5 times to twice as high as the nominal pressure of the working cylinder. On the other hand, the working cylinder has maximum damping capacity if the damping pressure has the maximum value throughout the damping stretch. Even theoretically, this ideal course of the damping pressure can only be achieved by the formation of the throttle cross sections and the throttle length between the damping element and the passage aperture if the same framework conditions are always maintained, in other words if the working cylinder, for example, is always moved at the same speed and moves the same mass. An attempt is then made, for the case of maximum speed and maximum mass, to obtain the ideal end position damping, so that the damping pressure no longer reaches the maximum value at lower speeds and lower masses.
Pressure medium-actuated working cylinders with end position damping are known from a number of publications. Thus, for example, EP 0 837 250 A2 shows a working cylinder in which the damping element has throttle grooves extending axially on its outer surface and tapering in their cross section. The throttle cross section over the throttle grooves becomes smaller and smaller as the damping element is inserted into the passage aperture. In addition to the throttle grooves, after the damping element is inserted into the passage aperture between the cylinder chamber and the cylinder connection, a pressure medium connection is switched on via a throttle point whose hydraulic resistance is largely independent of the depth of insertion of the damping element.
DE-OS 22 14 032 recites a pressure medium-actuated working cylinder. In this type of working cylinder, the outer surface of the damping element is rotationally symmetrical. In the known working cylinder, an entry whose effect is negligible for the end position damping, is adjoined by a surface section with a smaller diameter, which is followed approximately from the center of the damping element by a surface section with a larger diameter, which extends to the piston end of the damping element.
It is an object of the invention to develop a pressure medium-actuated working cylinder so that a high damping capacity is achieved, in other words so that a large mass can be braked over a short travel, without any expectation of damage caused by pressure peaks.
This object is achieved with a pressure medium-actuated working cylinder which additionally has the features of the invention. In a working cylinder according to the invention, then, viewed in the direction of insertion of the damping element into the passage aperture, the damping element has, before the section of smaller diameter, an average diameter which lies between the maximum diameter at the piston end of the damping element and the smaller diameter. This prevents the damping pressure falling rapidly again after a sharp rise at the start of insertion of the damping element into the passage aperture, so that it remains at a high level. The average diameter exists only over a short stretch relative to the length of the surface section of small diameter, which prevents the damping pressure exceeding the maximum admissible pressure, in other words prevents the working cylinder being damaged by pressure peaks. It has been found that, with the damping element constructed according to the invention, a course of the damping pressure close to the ideal curve can be achieved for a particular speed and mass.
According to features of the invention surface sections with, respectively, a fixed large diameter, a fixed small diameter and a fixed average diameter are provided. The diameter of the damping element thus does not change continuously during progression in the axial direction. The second surface section, according to feature of the invention, advantageously makes a transition into further surface sections with a diameter changing continuously during axial progression, into the first surface section and into the third surface section.